Because the entire audio system has been reworked.
List of changes:
Improved sound quality for all settings.
Improved sound quality for multi-channel sound systems (5.1; 7.1; and others).
Updated sounds for ship engines. Sounds are divided into two types—steam turbine and diesel, each with its own distinctive tone.
Updated sounds for aircraft engines.
Updated ambient sounds with the Ultra sound quality setting selected.
The SFX volume slider has been removed from the audio settings. Previously, the slider was used to control all non-musical in-game sounds, with the exception of voice messages. Thus it duplicated the other sliders located in the audio settings tab on the right-hand side of the screen.
A new "Damage audio volume" slider has been added. This is used to control the sound of shells' interaction with all surfaces and ships, and the effects they cause.
Added an option to adjust the volume of the horn that sounds when launching the game. It can be adjusted with the "Music in the Port" slider.
Because of the increase in quality, namely support 5.1 and 7.1 the settings had to be reset.
-Hapa